Thermoplastic liners for disposition within pipelines, either initially or as repair, for protecting the internal walls of the pipeline from deterioration, corrosion and the like, have been utilized in the past. For deteriorated, corroded or damaged pipes, the liners restore the fluid transport capability of the pipes, i.e., either gas or liquid, and prevents further interior deterioration. Liners of this type and apparatus and methods for forming and installing the liners are disclosed in U.S. Pat. Nos. 4,998,871; 4,986,951; 4,985,196; 5,112,211 and 4,863,365, of common assignee herewith, the disclosures of which are incorporated herein by reference. It has, however, been a continuing problem to provide an efficient, cost-effective method and apparatus for lining a main pipeline and one or more lateral pipes and sealing the liners in the main and lateral pipes to one another at their juncture. An effort to overcome that problem is set forth in U.S. Pat. No. 4,956,051. However, there is no systematic tying of pipelines by remote control which would provide an encapsulating pipeline system.
For purposes of the present description, it will be appreciated that in most pipelines, there is a main pipe which has one or more lateral pipes in communication with the main pipe at longitudinally spaced positions along the main pipe. In connection with the lining of gravity sewer pipes, the terms "main pipe" and "lateral pipe" or "laterals" are frequently used. In connection with the transmission of gases or fluids, for example, natural gas, for industrial purposes, the nomenclature typically refers to a main pipe and a branch pipe. As used herein, the term "branch pipe" is used synonymously with the term "lateral pipe" or "lateral" and thus these terms embrace both gravity sewer pipes, as well as industrial pipeline applications for the transmission of fluid or gas. Also, in these applications, the diameter of the pipe is typically equal to or less than the diameter of the main pipe. The term "encapsulating" means enclosing the system without excavation or access to the main line or branches and preventing inflow or outflow of any liquids in the pipeline.
It will be appreciated that at the juncture of an underground main pipe and a lateral pipe, there is an opening affording communication between the two pipes. It is known to line a main pipe with a liner of plastic material in accordance with any one of the above-identified patents, as well as to line a lateral pipe in accordance with a similar procedure. Also, the juncture of the main and lateral liners should be sealed to prevent ingress of gases, fluids or other materials into the lined pipes from sources external to the main and lateral pipes, as well as egress of the fluid or gas from the lined pipes at their juncture. Many pipes fined with plastic materials using the above-identified known methods employ a cutter to form the opening through the main pipe liner into the lateral pipe. However, there has been no effective way of fusing the lateral and main liners to one another at their juncture. Further, in those applications where flammable materials are transported in the main and/or lateral pipes, it is highly dangerous to employ equipment which generates sparks to seal the main and lateral liners one to the other. Such sparks could cause an underground explosion, even when the main and lateral pipes are purged of the flammable material, because residual flammable material oftentimes remains.